SO2+KCr2O7

Question

When SO2 is bubbled into a beaker of acidified K2Cr2O7 solution,which of the following statements about the reaction is correct?

A. SO2 bleaches acidifed K2Cr2O7
Why this is wrong?

B.The oxidation number of Chromium changes from +6 to+2

C.The colour of the solution turns green
Why this is wrong?

D. SO2 is oxidized
SO2唔會變左SO3-2先,一次過到SO42-?

ans:D

Answer 1

A is wrong.

SO2 bleaches by reduction. This is only correct when the reduced form of the dye is COLOURLESS.

However, the reduced form of dichromate is Cr3+ which is green.

So A is not correct.

B is not correct. The O.N. changes from +6 to +3

Actually i wonder why C is wrong. Prehaps you can say that in actual practical we can see "blue-green" rather than green

D is correct. SO2 is directly oxidized to SO42-

Answer 2

Actually , the redox reaction of SO2 is due to the SO3-2
Because when SO2 contact with H2O
it will form SO3-2 ions
So3-2 will be the reducing agent

so you are right ~
SO2 will first be changed into SO3-2 before redox reaction !
So the prsence of H2O in the solution is necessary for the reaction to occur!

2007-02-14 22:51:03 補充：
Overall , SO2 is oxidized~